Noble metal conductors made from thick film compositions containing a noble metal and a glass frit dispersed in a vehicle are well known in the electronics art. Beneficial characteristics such as low resistivity, good solderability and good adhesion to a ceramic substrate vary according to the particular ingredients selected. A useful composition containing a silver metal is described in U.S. Pat. No. 4,001,146. The high cost of silver and other noble metals has led to the search for other less expensive metals as conductors. Nickel and copper are in this category.
U.S. Pat. No. 3,943,168 describes conductor compositions containing nickel and a glass frit dispersed in an inert liquid vehicle. U.S. Pat. No. 4,072,771 describes conductor compositions containing copper and a glass frit dispersed in an inert liquid vehicle. Frit-bonded conductors, however, have generally been found to develop a glass-rich interlayer between the conductor and ceramic substrate after firing. This interlayer inhibits heat transfer between conductor and substrate and being brittle is subject to cracking during thermal cycling with concomitant loss of adherence. It is also a region of low electrical conductivity. Low conductivity is particularly deleterious in circuits operating at microwave frequencies of 1 GHz and above.